With volatile weather, powerful tides and bone-numbing temperatures, the English Channel is a formidable prospect for even the most accomplished swimmers. Tom de Castella follows hopefuls as they attempt the crossing to France. Photographs by Richard Ansett

At Samphire Beach, a Japanese woman stands in front of Dover's white cliffs. She is dressed in a pink and blue swimming costume, yellow cap and goggles. Her back, shoulders and thighs have been basted generously with Vaseline. After a minute or so, she waves to us and begins stepping awkwardly across the pebbles and into the English Channel. It is 10 past seven on a Tuesday morning. Most people will be having breakfast or getting ready for a day at the office. Miyuki Fujita is swimming to France.

There are six of us on the Suva, the boat that will accompany her on the 21 miles to Cap Gris Nez, the closest point to England on the French coast: pilot Neil Streeter, a co-pilot, an observer from the Channel Swimming & Piloting Federation, a galley hand, Miyuki's coach Haruyuki Ishii and me.

We watch as Miyuki wades out through the shallows before diving under a wave. If all goes to plan she will not leave the water for another 12 hours. We will average between one and two miles an hour, bobbing around like a bath toy in this most fickle of seas.

Swimming the Channel is one of the world's abiding natural challenges. Since merchant seaman Captain Matthew Webb first swam it – unaided – in 1875, only 900 people have successfully made it to the other side from about 7,000 attempts. There are other challenging swims around the world – the Cook Strait between New Zealand's north and south island, the Straits of Gibraltar, California's Catalina Channel. But the English Channel is the one with history, romance and global branding.

Four things make it so tough: powerful tides, the infuriating geography of the French coast, unpredictable weather and, above all, the cold – the water rarely rises above 15C. Webb swam breaststroke, which explains why he took 21 hours and 45 minutes to reach France. But the size of his achievement can be seen in the fact that it was 36 years and 70 further attempts before anyone else made it across. Between 1875 and 1949 there were four successful swims from England to France and 16 from France to England, which is easier but has now been banned by the French authorities (who do not want to encourage swimming from their side, and by banning it can argue that all swims must be controlled by the British). The sport really took off in the 1950s, and over the ensuing years a bewildering array of feats and records have been set, from swimming it butterfly to multiple crossings. In 1961 Antonio Abertondo from Argentina became the first person to swim it both ways non-stop, in a time of 43 hours and 10 minutes. Twnty years later, John Erikson trumped that with a three-way swim in 38 hours and 27 minutes.

Most are simply grateful to get across once. Six people have died trying. The most recent was Ueli Staub, a Swiss extreme sports enthusiast who disappeared in August 2001 on a wave in the dark just off Calais, not far from the end point. His body was found a few weeks later off the Belgian port of Ostend. It is thought he had a heart attack, perhaps caused by his caffeine-heavy feed pattern of strong coffee and flat Coca-Cola. Renata Agondi's death in August 1988 was the most controversial. The 25-year-old Brazilian died from exhaustion after her coach refused to let her leave the water. (Now the support boat's pilot, not the coach, has the final say.)

In 1954 there was the tragi-farcical death of Briton Ted May who couldn't afford a support boat. He swam towing an inner tube with his food and drinks inside, and despite one failed attempt, which ended in rescue, he tried again a few days later. The rubber ring was found floating in the Channel the next day and his body washed up on a Dutch beach soon afterwards. Other heroic failures lived to tell the tale. Jabez Wolfe reputedly tried to swim the Channel 22 times, starting in 1906, never making it despite three times getting within a mile of France. Lord Freyberg, Governor General of New Zealand between 1946 and 1952, made a number of unsuccessful attempts as a young man. During his best effort, he was only 200 yards from land when he stopped to rest before one final push. Seeing his exhaustion, his wife leant over the side of his support boat and gave him a fortifying slug of brandy. And that was that. He went straight to sleep and had to be pulled out.

The global cachet of the Channel is astounding, and swimmers are drawn from around the world to take it on. At a youth hostel in Dover I meet the Kedia family from Amravati in the state of Maharashtra, India – about as far from the chilly waters of south-east England as one can get. They are hoping to see their second daughter Ritu, 17, triumph over the Channel just as their eldest, Barkha, did in 2001. For Mr. Kedia, an aluminium factory owner, the swim is not just a sporting achievement, but an investment, a status symbol. Conquering the Channel helped Barkha secure a place at a good university, and even led to her being invited to Delhi to receive a National Adventure Award from Prime Minister AB Vajpayee. The cost of transporting his family to Kent for two weeks is considerable (even the Channel crossing itself costs an average of £2,100 – mostly to cover a boat and pilot), but Mr. Kedia believes it is worth it. 'It's so important to have self identity,' he explains. 'I am known in the city for my swimming girls. My dream is that both my daughters will go to great heights.'

Ritu recalls her sister's attempt: 'When Barkha did it in 2001 the weather was really bad and I was seasick on the boat. But I knew that I was going to do it one day. When you do it, you learn so much.'

Part of the Channel's appeal lies in the fact that Webb's tradition has been upheld by strict rules. He was not the first man to swim the Channel: the American Paul Boyton beat him to it in an inflatable rubber suit with built-in paddles and a sail. But Webb (who later died attempting to swim the rapids and whirlpools beneath the Niagara Falls) was scornful of synthetic aids and it is his purist stance that has been kept alive. Trunks, goggles, Vaseline, a feed from time to time, and that's it. Doing it in a wetsuit doesn't count. Anyone can apply, as long as they can provide written evidence they have done a six-hour swim in water of 16C or less.

There used to be just one governing body responsible for ensuring people abided by the rules – the Channel Swimming Association, which was founded 80 years ago. But in 1998 the committee split and half the members left to set up a rival body, the Channel Swimming and Piloting Federation (which is now by far the more popular of the two). The old guard at the CSA feel they have been betrayed and refuse to acknowledge the CS&PF's swims, unlike the latter, which recognises both its own and the Association's swims.

Mike Oram, the honorary secretary of the Federation, says his role is far more than just a bureaucratic one; he is also one of the swimmers' chief motivators. He was piloting the support boat of Christof Wandratsch when the 38-year-old German crossed the Channel in 2005 in a record time of seven hours and three minutes. 'After four and a half hours he stopped and said he wanted to get out,' Oram says. 'We spent 15 minutes arguing – I told him my reputation was on the line. He needed me to make him mad.'

There is one place where you can always be sure to find a handful of Channel swimmers, and that is beside the icy water itself at the Varne Ridge Caravan Park, dramatically perched on the cliffs between Dover and Folkestone. About 125 people will attempt to swim the Channel solo this year and, for many, this will be their base camp. There is a colourful mural marking the dozens of swimmers from around the world who have stayed here, with flags, dates and swim times. Here I meet Geoff Evans and Steve Payne, from Australia's Blue Mountains who have brought their families over to cheer them on.

Evans, a 44-year-old glassmaker, says the Channel is the 'bee's knees of swimming'. His friend Payne, 47, had made two previous attempts, which failed due to sickness, and his stories inspired Evans. 'I talked to my wife and she said, "OK, you can do it – I need a holiday anyway," so we all came over.' For the past 14 months he has been averaging swims of 25km a week and has done three 24km swims in the cold (16C) waters of the Pacific at Woollongong. He has been eating well to compensate for the cold, he says, patting his belly admiringly: 'The second part of my training is going down the pub for a Guinness,' he laughs. For Payne, a firefighter from Kurrajong, it's a case of third time lucky. 'I couldn't wait to get back. I've done 28 Ironman events but I consider the Channel the biggest challenge of them all.' They have both been in Dover for three weeks, waiting for the weather to improve.

In another caravan I meet Enrique Flores, a Mexican civil engineer hoping to raise £10,000 for children's charities. 'Not all children are as fortunate as my own,' he says. Later, I get chatting to the Lewis family from Coniston in Cumbria, who are supporting their 23-year-old daughter Becky on her first swim.

Becky has been swimming competitively since the age of five. 'The Channel is something I have always wanted to do, even when I was tiny and didn't know exactly where it was,' says Becky, a physiotherapy student at Teesside University. 'Since becoming an open-water swimmer and competing in long swims, I realised it was within my grasp.' She has been in training since last September, often swimming eight miles a day, in Coniston Water near her house, the local pool and in the Irish Sea. She usually eats a balanced diet, but the week before her swim she bulked up on carbs with pasta and jacket potatoes. Channel swimming is one of few sports where a bit of body fat and a stocky physique are seen as a good thing.

Miyuki Fujita is a 41-year-old housewife from Japan's Aichi province who helps out in her husband's sweet-making business. So why her obsession with the Channel? 'I don't want to be like other people. I started off swimming in the sea and it escalated, and that's how I find myself in Dover,' she says, as if it's the most natural thing in the world. She has now swum the Channel three times after two failed attempts, and is one of only 16 Japanese to have swum it.

At five to eight, Miyuki is thrown a bottle. She drinks underwater to avoid the waves catching her by surprise, then tosses the bottle back, all within about 10 seconds, and then she is off again, repeating the process every 40 minutes. The drink – a 300ml mixture of carbohydrate solution, vitamin B2, glucose and Japanese tea – is a far cry from the old days when swimmers refuelled on a ham sandwich, cup of warm ale, some cod liver oil, or a slug of brandy.

Miyuki is taking it slow and steady. Whenever she drops her pace, the pilot puts the engine into neutral and we idle until she pulls ahead of us again. By half past nine she looks stronger than she did at the start, her rhythm more measured. The wind picks up sharply.

Just after 10, we approach the first shipping lane, a one-way procession of container ships. The Channel is believed to be the busiest waterway in the world, with 5,000 people afloat at any one time, adding a man-made frisson of danger to what is essentially a battle against nature (though the pilot boats communicate on their radios with coastguards to avoid catastrophes).

At midday, the white cliffs behind us appear to have barely receded, and ahead the low dark smudge of France seems no closer. A couple of curious gulls circle the boat and land close to Miyuki, momentarily breaking the monotony. By now, her body will have started converting fat to glycogen, which provides energy, and the pain will be kicking in (when endurance athletes talk about 'hitting the wall', that's the point at which their glycogen levels run out). Miyuki's small body is knifing its way through the grey-green seascape. The power comes from the shoulders. The kick is at first glance puny, but never misses a beat. Her face when it turns upwards for air shows an expression of confidence. Her eyes, even though she is wearing goggles, will be stinging by now, her tongue thick with salt, her feet like blocks of ice.

I recall a conversation I had with Greg Whyte, a professor of sports science at Liverpool John Moores University, and the man who coached the comedian David Walliams to Channel-swimming glory last year. Whyte had his own Channel story, an attempt that looked to be heading for a time of under eight hours – two hours faster than Walliams – until a couple of miles off the French coast the tide got him, as it gets so many swimmers as they reach the closing stages. After two and a half hours of going nowhere he had to be pulled out. 'The cold creates a misery, which you try to psychologically park on one side,' he said. 'But it never goes away and as you start to get fatigued it allows negative thoughts to enter your head.'

It is just gone one o'clock and it's an angry sea now, a 15-knot wind cutting across the surface. Rollers are coming over from our right – it is a sou'wester, just what every swimmer dreads. But Miyuki seems unaffected. Not for the first time, I am finding it hard to appreciate the appeal of the Channel swim. There is a miserable drudgery to it all. These people are not just physically and mentally tough – they are a bit mad, too.

A former currency trader, Alison Streeter – Neil's sister – is the so-called Queen of the Channel, with 43 crossings to her name (more than anybody else), including a three-way that took 34 hours and 40 minutes. She sums up its attraction. 'The Channel is like a living, breathing animal and is different every single day, so every swim is unique,' she says. 'I have done plenty of other swims around the world but none has the same history or excitement.'

Laura Mahady, a lecturer in sports psychology at the University of Aberdeen, says that extreme athletes are often conformists who use sport to express their obsessive-compulsive side. Amanda Williams, a reader in clinical health psychology at UCL and a former champion free-diver, says endurance sport is about small degrees of improvement: 'All of these things you do by increments, working up a small amount each time, all of it manageable.' For David Shearer, a lecturer in sport and exercise psychology at Swansea University, it is about focus: 'Endurance athletes tend to be very process-oriented. They focus on what they are doing and on the end goal.'

A few weeks earlier, I had met Petar Stoychev, an intense 30-year-old Bulgarian, and a former world champion marathon swimmer. Last summer he had attempted to beat Christof Wandratsch's record, but in storm conditions he missed out by 18 minutes. He was waiting in a B&B in Dover with his coach and two Bulgarian television journalists, hoping for a break in the weather. 'This is the oldest and hardest swim in the world,' he told me. But there was something else driving him on, too – the stopwatch. 'Mine is a sport without records. During the World Cup races it is important to win, but the time doesn't matter. [Everyone swims at the same time and winning is all that counts.] But with the Channel, a world record exists.' Stoychev is tall and lean with not a pinch of fat on him, unlike most Channel swimmers. But because he swims so fast – averaging 3mph, almost Olympic speed, at his quickest – his lack of bulk is not an issue. 'Most Olympic swimmers can't do it in cold water,' Mike Oram tells me later. 'They are lean machines, used to swimming at 27C over short distances.'

There is a rumour in Dover that the Russians are coming – two expert swimmers, Yuri Kudinov and Natalia Pankina, both highly rated and chasing the record. So is Stoychev worried- 'I'm afraid of nobody,' he says in a slightly robotic voice, with a hint of Arnie's Terminator. 'I'm just afraid of bad weather.'

It is about four o'clock and for the first time Miyuki stops and looks disorientated. She has hit a bank of seaweed and grinds to a halt, wary of jellyfish lurking underneath. Ishii barks at her to carry on. She obeys.

Two and a half hours later and the coast of France is lit by evening sun. I feel strangely elated, but then Neil Streeter appears on deck with bad news. The tide has turned and we're not going to make Cap Gris Nez. Sure enough, the famous lighthouse is beginning to slip away to our right as we follow Miyuki. It must be a crushing blow to any swimmer's confidence, but Miyuki ploughs on uncomplainingly. We should be half an hour away from France but rather than getting closer, the land is receding while we are swept in the direction of Calais.

Two hours later, Ishii says we are a mile and a half away from the village of Wissant and its sandy beach. Miyuki is still going but looks tired. The end is in sight, but many others have come this far and failed. At five past nine with the pink sun setting behind us, Miyuki makes her approach to the beach. There is momentary confusion on board about how they are going to time her arrival. It's too shallow for the boat to go in any further, land is still a few hundred metres away and darkness is closing in. Ishii ends up diving into the water and trying to catch up. The pilot's assistant can't see Miyuki through his binoculars. Finally, she is spotted and her time logged at 13 hours and 59 minutes. On the beach we can see flashbulbs going off as Miyuki and Ishii celebrate with several locals. Miyuki then has to swim back to the boat as night is falling. On board, she huddles up under some blankets and goes to sleep as Streeter points us towards England. The return trip, thankfully, will take only a couple of hours.

Two weeks later, I catch up with the swimmers. Evans and Payne, the two Australians, tell me that they failed in their attempts. Evans pulled out after four and a half hours, defeated by cramp in his left leg. 'When the pilot mentioned that I was going backwards, I lost any confidence I had and felt it was time to get out,' he says. Payne pulled out an hour later. He had managed to conquer his sickness this time, but succumbed to intense pain in his shoulder. Undeterred, they have vowed to return in two years' time.

Becky Lewis, Enrique Flores and Ritu Kedia all succeeded, Lewis in an impressive time of nine hours, 35 minutes. 'I was really pleased with my time,' she says. 'I was very nervous and it took me two hours to settle down, but the cold didn't bother me much until the end. When I got to the beach I was too tired to get emotional. I've now got the bug and want to try again in 2009 – I know there are things I could do better.'

I meet Miyuki and Ishii again, who are preparing to return to Japan. She is pleased that nothing went badly wrong but is disappointed with her time, and is already planning another attempt for next summer. She says she didn't feel cold, but suffered cramp in her thigh. The south-westerly wind and waves slowed her down, Ishii says. She kept herself going by singing Japanese pop songs and trying to recall the nice e-mails people had sent her. Ishii shows me a map of her swim, a sweeping back-to-front 'S' shape reflecting the tide's huge influence. Miyuki says it was choppier than last time, but at least there weren't so many jellyfish. 'The hardest bit is seeing France and not being able to reach it, seeing yourself drifting, that was the toughest.' So when did she actually know she would make it- 'Not until I was standing on the beach,' she smiles.

Petar Stoychev was defeated by July's bad weather, but returned to Dover last month. On August 24, 132 years to the day since Captain Webb's crossing, he broke the world record with the first ever sub seven-hour swim, reaching Cap Gris Nez in six hours, 57 minutes and 50 seconds.

Some people, it seems, just don't know when to give up. And that is what sets Channel swimmers apart from the rest of us. They understand better than anyone the true meaning of the phrase inscribed on Captain Webb's memorial stone in Dawley, Shropshire: 'Nothing great is easy.'